In cold climate regions like Canada, a predominant amount of energy expended in residential housing (65%) is spent for space heating. Efforts have been made to get a portion of this space heating energy from solar radiation. Various solutions have already been proposed in the prior art to use solar energy for house heating. Typically heat can be generated from solar radiation in different types of thermal solar collectors and systems like; vacuum tube collectors, flat plate collectors, Trombe wall or solar wall. The most efficient, in terms of heat generation, are vacuum tube collectors and flat plate collectors. These collectors are usually used for hot water generation, as they are too expensive to be used for space heating. It is known that utilization of solar energy for house space heating involves two basic types of thermal solar systems—active and passive.
Active Systems
A typical active system uses a glazed flat thermal collector. During a heating period (day), solar radiation is converted into heat and the generated heat is transferred with circulated liquid to a central heat storage tank (e.g. water tank). During a demand time (night), the accumulated heat is redistributed by a heating system which circulates heated fluids. Such solutions require a system that consists of the solar collectors, a network of pipes, a heat storage tank, a fluid circulating pump, control valves and controllers inside a building. The systems are complex, and involve costly installation of the network of pipes with fluid circulating pump. The systems are prone to freezing when exposed to freezing temperatures, unless expensive liquids are used. In some active systems, heat can be transferred with forced circulating air systems (as described in U.S. Pat. No. 4,197,993), but because of the low heat capacity of air, such systems are limited for ventilating purposes.
The active system has a certain number of drawbacks. They are:                relatively complex and feature a costly system of pipes, heat storage, heat control and heat redistribution systems        need for pumps and energy required for pumping        operational problems with leakage and/or plugging (maintenance).Passive Systems        
Passive systems are simpler and cheaper and, therefore, becoming more and more popular. However, they have lower efficiency. In a typical passive system, solar energy is collected by a thermal energy collector combined with a wall and transferred by conduction to the house wall for storage. In such systems, a solar radiation absorption layer often is combined with a glazed enclosure and a heat trap to reduce heat losses and improve efficiency. The simplest and best known solution of this kind of system is the Trombe wall. The Trombe wall solution consists of a transparent cover and an absorption layer deposited on a heat transmitting and accumulating material like concrete, bricks or other masonry type of walls. Heat generated during exposure to solar radiation is stored in the wall and transferred through the wall to the building interior. A typical Trombe wall consists of a 200 to 400 mm thick masonry wall (or concrete) coated with a dark, solar radiation absorbing material and covered with a single or double layer of glass. The space between the glass enclosure and masonry (collector) is from 20 to 50 mm. The solar radiation passes through the transparent glass and is absorbed by the dark surface of the absorber and slowly transferred inward by conduction through the masonry. It takes about 8 to 10 hours to transfer heat to reach the interior of the building for a 200 mm thick Trombe wall; thus, a Trombe wall absorbs and stores heat for evening/night use.
In passive systems, collected heat is transferred to the wall to material that is characterized by large thermal mass (masonry, bricks, concrete) and is heat conductive. The masonry type of wall required for heat storage (as the thermal mass) is typically a poor thermal insulator. During prolonged cold nights, or cold, cloudy days, such walls experience significant heat losses. As a result, the application of such systems in cold regions (e.g. Canada) is not practical.
The prior art features several attempts to improve the ability to collect heat, reduce energy losses and increase performance. One such solution is described in U.S. Pat. No. 4,323,053, where a solar collector is equipped with an integral heat trap in a transparent wall. The solar radiation absorber is arranged to collect incident solar radiation passing through the front enclosure.
In another, similar solution, developed by Energiesysteme Aschauer Ltd. in Linz, Austria, a heat trap in a form of cellulose comb is positioned between the glazing and a heat-storing wall. This solution combines the thermal insulation ability with direct heat storage in the wall. However, this kind of wall still lacks sufficient thermal insulation for cold climate regions. Thick cellulose layer blocks allow efficient heat transfer into a heat accumulating wall that on its own has limited thermal insulating value.
U.S. Pat. No. 4,237,865 (Lorentz) describes a solar heating siding panel which includes double panels of clear glass secured in a housing horizontally spaced outwardly of the building. Inside of the housing is located a heat collector. The collector, in the form of an air gap, is closed on the inside by a heat exchanger of substantially thin foil material and spaced inside the glass panels. A system of temperature controlled hinged dampers at the bottom and at the top of the collector passages release a flow of air to heat a room. This system requires complex thermally controlled dampers and does not have any heat storage capacity.
WO patent 99/10934 has a combined photovoltaic/thermal panel that is provided with one or more flow channels, for the purpose of delivering thermal energy during operation to a fluid flowing therein. The PV and thermal collectors have been joined to form a single assembly with the interposition of a metal-containing plastic material having bonding properties. U.S. Pat. No. 4,587,376 describes another combined photovoltaic/thermal solar collector in which a light-permeable superstrate (PV) and a metallic substrate (thermal) are used. These solutions require a structure, which is relatively complex and costly.
A Canadian company, Conserval Engineering Inc., has developed a “SolarWall” technology that is a building integrated collector in the form of a facade or roof element. The solar energy is collected using perforated absorber plates that are mounted in such a way that cold ambient air is allowed to pass behind the perforated panels in a uniform way. Heat generated from the solar energy is transferred to the air, which is used for heating ventilation air. This solution has no capacity to store heat for evening/night use.
An unglazed porous solar collector is sold under the Trade Mark brand name of “SolarWall″”. It absorbs the sun's energy and uses it to heat the air that is pulled through the collector surface and into the air distribution path connected to the mechanical system of the building. With SolarWall, air passes through channels between a wall of a building and a solar radiation absorbing layer; however, due to the lack of glazing, the very low thermal capacity of air and low thermal conductivity, such solutions are not very efficient and usually are used to heat air.
In general, prior art solutions require either complex fluid circulating systems feature applied in combination with well insulating walls or simpler passive solutions with direct wall (masonry) heat storage that have limited insulating value and loose a lot of heat when cold, thus limiting their scope of application.